1. Technical Field
The present invention relates to a semiconductor device, more specifically to a device for generating a transmission clock in a sink without a reference clock and a method of transmitting data from the sink to a source by use of the generated transmission clock.
2. Background Art
With an increased speed of data transmission, a source now transmits a clock and data at the same time, and a sink now recovers and uses the clock. In this high-speed communication method, a clock data recovery (CDR) of the sink is responsible for recovering the clock and aligning the phase of the recovered clock. Although high-speed data transmission is possible from the source to the sink, the source and the sink communicate through one or more unidirectional channels. Some communication methods include a unidirectional channel, which transmits the data from the sink to the source, or a bidirectional channel between the source and the sink. Nevertheless, the data transmission speed of the bidirectional channel is relatively lower than that of the unidirectional channel. Besides, both the source and the sink have to each include a configuration for generating an additional transmission clock for bidirectional data transmission. While a reference clock is usually provided to the source, it is often uncertain whether a reference clock is provided to the sink. Accordingly, when a sink is produced, it is imperative that the sink is designed to prepare for the absence of a reference clock. Moreover, if the number of channels is increased, it becomes difficult to arrange the large number of channels efficiently.
The related arts are disclosed in U.S. Pat. No. 7,263,153 and U.S. Pat. No. 7,839,965.